We study the effects of gender board diversity on firm performance. We use novel and rich firm-level data covering over 400 thousand private and public firms spanning the years 1995-2020 in Europe. We augment a standard TFP estimation with firm fixed effects to explore the role of gender board diversity. We construct a shift-share instrument for gender board diversity and find that increasing the share of women on boards is conducive to better economic performance. The results prove robust to a variety of sensitivity analysis. This outcome is driven primarily by firms from the service sector and by smaller firms. The impact was stronger during the early years of our sample.